Pluto Who? Astronomers Find Evidence for “New” Ninth Planet

The surface of the dwarf planet Pluto, taken by NASA’s New Horizons spacecraft in 2015 [Image: ‘First Ever High Resolution View of Pluto’s Surface’ under a CC BY 2.0 license]It sounds like it belongs in a sci-fi B movie from the 1950s, but a growing body of evidence suggests that “Planet Nine” is the ninth planet in our solar system…if it actually exists. Astronomers Konstantin Batygin and Michael Brown recently observed that the orbits of several small, rocky objects beyond Neptune were arranged in an unexpected manner. In fact, their alignment is so strange that there’s only a 1-in-14,000 chance that it arose purely by coincidence. Batygin and Brown have proposed that the gravit-ational pull of an object many times larger than Earth – Planet Nine – is responsible for these peculiar paths around the sun.

We have yet to directly observe Planet Nine, but history tells us that we may be on the right track: analogous calculations on Uranus’ orbit led to the successful prediction and discovery of Neptune in the mid-1800s. So why haven’t we seen this “new” planet? Even though Batygin and Brown have calculated Planet Nine’s orbit, we don’t know where along that lengthy path to point our telescopes. To complicate matters further, Planet Nine is projected to fluctuate between 20 billion and 100 billion miles away from the sun, well beyond the 4.6 billion-mile mark that Pluto never crosses. Nothing short of direct telescopic observation will allow astronomers to conclude if Planet Nine truly deserves to be called a “planet” or if it’s just another wannabe.

Acknowledgments: Many thanks to Lauren Woolsey, a Ph.D. candidate in the Astronomy Department at Harvard University, for providing her expertise and commentary on the topic.